Net revenues for the quarter ended December 31, 2012 of $8.3 million decreased 23% from the third quarter revenues of $10.8 million. Fourth quarter 2012 end user net revenues were $7.0 million or 84% of net revenues, compared with third quarter end user net revenues of $9.0 million. OEM net revenues were $1.3 million or 16% of net revenues compared with third quarter OEM net revenues of $1.8 million. Net revenues from markets outside of semiconductor tests were $1.3 million or 15% of net revenues compared with $1.1 million, or 10% of net revenues in the third quarter.
Thermonics' fourth quarter 2012 revenue was $1.2 million, which was down slightly from the level achieved during the third quarter. As Bob mentioned earlier, at the end of the fourth quarter of 2012, our Thermal Products segment introduced the new ATS series of ThermoStream(R) products, which incorporated the best features of the Temptronic and Thermonics Forced Hot Air System. Therefore, going forward, we will no longer break out Thermonics revenues as the product lines have been consolidated.
The Company's overall gross margin for the fourth quarter was $3.5 million or 42%, as compared with$4.8 million or 44% in the third quarter of 2012. The reduction in gross margin was driven by a less favorable absorption of our fixed manufacturing costs in the fourth quarter, which increased to 20% of revenues in the fourth quarter from 15% of revenues in the third quarter. While our fixed manufacturing cost increased as a percentage of revenues quarter over quarter, they were essentially flat quarter over quarter at $1.6 million.
The increase in our fixed manufacturing costs as a percentage of net revenues in the fourth quarter was almost fully offset by a reduction in our consolidated material costs, which declined from 37.0% in the third quarter to 32.4% in the fourth quarter. All three of our product segments experienced decreases in their component material costs quarter over quarter, with our Electrical Products segment experiencing the largest reduction, from 45.5% of net revenues in Q3, to 37.3% of net revenues in Q4. The reduction was driven by a change in product mix in our Electrical segment, as well as in our other two product segments. Our Thermal Products segment's component material cost decreased from 33.0% in Q3, to 30.3% in Q4, while our Mechanical Products segment declined from 39.5% in Q3, to 36.8% in Q4.
I will now discuss the breakdown of operating expenses for the quarter.
Selling expense for the fourth quarter was $1.1 million or 14% of net revenues, compared with $1.3 million or 12% of net revenues for the third quarter, a decrease of $180,000 or 14%. The decrease was primarily due to reduced levels of sales commission on lower revenue.
Engineering and product development expense was unchanged quarter over quarter, at $1.0 million, which represented 12% of net revenues in Q4 compared to 9% of revenues in Q3.
General and administrative expense for the fourth quarter was $1.3 million or 16% of net revenues, compared to $1.4 million or 13% of net revenues in the third quarter, a decrease of $116,000 or 8%. The decrease was primarily the result of reduced accruals for profit-related bonuses on lower profits in the fourth quarter and lower levels of professional fees.
Other income for the fourth quarter was $21,000 compared to $23,000 for the third quarter.
We booked an income tax benefit of $83,000 in the fourth quarter, compared with income tax expense of $348,000 at the third quarter. The income tax benefit booked in the fourth quarter was driven by the year end true up of our deferred tax assets.
Our effective tax rate in the fourth quarter was 70%, compared to 34% in the third quarter. We expect our effective tax rate will remain in the mid 30% range throughout 2013. At December 31, 2012, we had total deferred tax assets of $2.0 million.
Fourth quarter net income was $201,000 or $0.02 per diluted share, compared with third quarter net income of $664,000 or $0.06 per diluted share. Average shares outstanding were 10,344,000 at year end, down slightly from the level at September 30, 2012.
Consolidated headcount at the end of December, which includes temporary staff, was 142, a decrease of four individuals during the fourth quarter. As we have noted before, we closely monitor our resource levels and will adjust as needed when we see any prolonged softness in demand. I will now turn to our balance sheet.
Cash and cash equivalents at the end of the fourth quarter were $15.6 million, up $876,000 from September 30th. During the fourth quarter, we paid a one-time dividend of $0.08 per share, which used $834,000 of cash. We currently expect cash and cash equivalents to increase sequentially throughout 2013.
Accounts receivable at the end of the fourth quarter was $5.5 million, which decreased $1.4 million during the quarter. The decrease was driven by a lower level of net revenues in the fourth quarter compared to the first, as well as a decrease in days sales outstanding, which were 58 days at December 31, 2012.
Inventory declined by approximately $708,000 to $3.1 million at the end of December. And capital expenditures during the fourth quarter were $148,000, compared to $154,000 in the third quarter.
Bob provided the consolidated segment booking data earlier in the call, but for the quarter ended December 31st, Thermonics bookings were $994,000, compared to $1.2 million in the third quarter. The backlog at the end of the fourth quarter was $4.2 million, up from $3.2 million at the end of the third quarter, and Thermonics backlog was $315,000 at December 31, 2012.
In terms of our financial outlook, as quoted in our earnings release, we expect that net revenue for the quarter ended March 31, 2013 will be in the range of $8.0 to $9.0 million, with financial results ranging from a net loss of $(0.02) per diluted share to net earnings of $0.03 per diluted share. We currently expect that our Q1 2013 material cost as a percentage of net revenue will range from 33% to 35% due to a more favorable product mix. Please note that our outlook is based on 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.