Net revenues for the quarter ended March 31, 2011 was $11.7 million, an increase of 23% compared with the first quarter of 2010, where net revenues were $9.5 million and 16% of our fourth quarter net revenues of $10.1 million. First quarter end user net revenues were $10.1 million or 86% of net revenues compared with fourth quarter 2010 end user net revenues of $9.1 million or 90% of net revenues. OEM net revenues were $1.6 million or 14% of net revenues compared with $1.0 million or 10% of net revenues in the fourth quarter of 2010. Net revenues for markets outside of semiconductor tests were $2.3 million or 20% of net revenues compared with $2.1 million or 21% of net revenues in the 2010 fourth quarter.
On a product segment basis, first quarter net revenues for the Mechanical product segment were $5.0 million or 43% of net revenues compared with fourth quarter 2010 net revenues of $3.6 million or 36% of net revenue. Our Thermal products segment had net revenues of $5.4 million or 46% of net revenues compared with fourth quarter 2010 net revenues of $5.1 million or 50% of net revenues. Finally, our Electrical product segment reported net revenues of $1.3 million or 11% of net revenues compared with fourth quarter 2010 net revenues of $1.4 million or 14% of net revenues.
The Company's overall gross margin for the first quarter was $5.1 million or 44% compared with fourth quarter 2010 gross margin of $4.8 million or 47%, and $4.5 million or 48% in the first quarter of 2010. The decline in the gross margin was largely due to higher than expected material cost which were the result of a less favorable product mix in both our Thermal and Mechanical product segments.
Our material cost for the first quarter of 2011 was 37.0% of net revenues, up from 33.6% in the fourth quarter of 2010. In our Thermal products segment, where our material costs increased from 25.2% of net revenues in the fourth quarter to 29.2% in the first quarter. The increase in material costs was due to an adjustment recorded during the fourth quarter of 2010 that related to material cost that had been over-accrued in prior quarters related to the leasing of Thermal Systems in Europe which caused the quarter over quarter comparison to be unfavorable.
In our Mechanical product segment, where our material cost increased from 43.4% in the fourth quarter to 45.3% in the first quarter, we saw our manipulator products, many of which have lower gross margin, increased from 20% of Mechanical product segment's net revenues in the fourth quarter of 2010 to 30% of this segment's revenues in the first quarter of 2011. We see this trend, with a less favorable product mix causing higher material cost, continuing into the second quarter of 2011 - and I will address this further when I provide my second quarter 2011 earnings guidance later in this call.
In addition to the increase in material costs, our gross margin in the first quarter was also negatively impacted by accruals for excess and obsolete inventory which were $86,000 or 0.7% of net revenues in the first quarter of 2011 compared to a net credit of $(77,000) or (0.8)% of net revenues in the fourth quarter of 2010. Our fixed manufacturing costs also increased during the quarter from $1.7 million or 17% of net revenues in the fourth quarter to $1.8 million or 15% of net revenues in the first quarter, an increase of $88,000 or 6%. The increase in fixed manufacturing costs was the result of increased salary and benefit expense, as well as additional rent and maintenance cost associated with the move of our domestic and Mechanical and Thermal operations during the first quarter. These move-related costs were $74,000 included in cost of sales. We had a total of $128,000 in move-related costs during the first quarter with the balance of these costs sitting in general and administrative expense.
I will now discuss the breakdown of operating expenses for the quarter.
Selling expense for the first quarter was $1.4 million or 12% of net revenues compared with $1.3 million or 13% of net revenues for the fourth quarter of 2010, an increase of $95,000 or 7%. The increase was primarily the result of increased accruals for product warranty expense due to the higher revenue levels, as well as higher levels of travel and advertising expenses. First quarter engineering and product development expense was $813,000 or 7% of net revenues compared with $789,000 or 8% of net revenue in the fourth quarter, an increase of $24,000 or 3%. The increase was the result of the increased spending on patent legal costs, higher levels of salary and benefit expense and increased travel cost. These increases were offset by reductions in spending on research and development materials and third party consultants who we engaged with to assist us in product development.
General and administrative expense for the first quarter was $1.6 million or 14% of net revenues compared with $1.3 million or 13% of net revenues in the fourth quarter, an increase of $289,000 or 22%. The increase in G&A expense is related to several items including increased levels of professional fees, higher levels of salary and benefit expense. In addition, during the fourth quarter of 2010, we had a net credit or recovery for bad debt expense of $86,000, which had reduced the fourth quarter's expenses, and there was no bad debt expense or recovery during the first quarter of[2011]**. Also included in G&A expense for the first quarter was $54,000 of third party moving cost. This is in addition to $78,000 we had incurred under G&A expense during the fourth quarter of 2010 in preparation for the move of our Thermal and Mechanical operations which were completed during the first quarter. Other income for the first quarter was $56,000 compared with $61,000 for the fourth quarter. Other income for the first quarter included a gain on sale of fixed assets of $40,000 compared to a $55,000 gain on sale of fixed assets included in the fourth quarter. The fixed asset sales in both periods were related to the move of our Mechanical products segment operations in New Jersey.
For the first quarter, we recorded income tax expense of $60,000, with an effective tax rate of 4.6% compared with income tax expense of $131,000 for the fourth quarter, which had an effective tax rate of 9.2%. The income tax expense recorded during the first quarter represented domestic state income tax expense on our earnings. We currently expect to have an effective tax rate of approximately 4.5% for the balance of 2011. At the end of the first quarter, our federal net operating loss carry-forwards was approximately $4.1 million and our state NOLs range from approximately $178,000 to $3.0 million, depending on the state in question. We have fully utilized our NOLs in the States of Massachusetts and New Jersey.
First quarter net income was $1.3 million or $0.12 per diluted share compared with 2010 fourth quarter net income of $1.3 million or $0.13 per diluted share. As I noted previously, the total move cost included in the first quarter results were $128,000 or $0.01 per diluted share.
Consolidated head count at the end of the first quarter, which includes temporary staff was 130 compared with 129 at the end of the fourth quarter. As we have noted before, we closely monitor our resource levels and adjust as needed if we see any prolonged softness in demand levels, and with the operational economies we have developed we continue to see no necessity of significant increases in personnel as business ramps.
I will now turn to our balance sheet. With demand fluctuations being the norm in our business, it is critical that we always strive to strengthen our balance sheet so that in down markets we can continue to strategically invest in key R&D and growth initiatives.
Cash and cash equivalents at the end of the first quarter were $5.2 million. This compares with $6.9 million reported at December 31st. The decrease in cash during the first quarter was caused by several factors including the investments in improvements in equipment for our two new facilities occupied during the first quarter, the payment of various accrued expenses and increases to our inventory. In addition, our sales in the first quarter of[2011]** were more concentrated in the latter part of the quarter. We currently expect cash to grow sequentially throughout 2011.
Accounts receivable was $8.8 million at March 31, 2011, an increase of $2.6 million from December 31, 2011. The increase was driven by increased sales and their concentration in the latter part of the quarter. In addition, we experienced an increase in our days sales outstanding, which increased from 48.6 at 12/31 to 63.0 at 3/31. While our customers are clearly taking longer to pay us this quarter, we do not expect any increase in bad debt expense or write-off as a result of these delinquencies.
Inventory at the end of the first quarter of 2011 was $4.0 million compared with $3.5 million reported at the end of the fourth quarter. The increase in inventory was due to purchases of material to be used for second quarter shipments.
Capital expenditures during the first quarter were $574,000 compared with fourth quarter capital expenditures of $575,000. Our capital expenditures during both periods were abnormally high and included leasehold improvements and equipment purchased in connection with our facility relocation. In addition, in both quarters, our capital expenditures included Thermal segment inventory which was converted to fixed assets representing equipment which we are leasing to certain customers in Europe as well as test fixtures purchased for our Electrical product segment.
As Bob noted earlier, bookings for the first quarter were $13.1 million and bookings from markets outside of semiconductor tests were $2.3 million or 18% of first quarter bookings. This compares with 2010 fourth quarter bookings of $11.7 million with bookings from markets outside of semiconductor tests of $2.3 million or 20% of fourth quarter bookings. The backlog at the end of the first quarter was$ 7.5 million compared with $6.1 million at the end of the fourth quarter.
In terms of our financial outlook, as noted in our earnings release, we expect that our net revenue for the second quarter ended June 30, 2011 will be in the range of $12.5 to $13.5 million and that net income will be in the range of $0.15 to $0.20 per diluted share. Our first quarter EPS guidance includes the impact of $75,000 of one-time cost associated with the preparation of the S-3 Shelf Registration we filed with the SEC earlier today. In addition, as I noted earlier on the call, we expect our product mix in the second quarter will be less favorable, with an expected material cost of approximately 200 basis points higher than we experienced in the first quarter of 2011. We currently expect these costs to return to more historically normal levels in the 33% to 36% range in the second half of 2011. Although achieving this goal is dependent upon the product mix ordered by our customers, and our ability to further cost down our existing product, please note that our outlook is based upon the company's current views with respect to operating and market conditions and customer forecast, which are subject to change.
Operator, that concludes our formal remarks. We can now take questions.