Our cost of goods sold increased year-over-year primarily as a result of the increase in revenues and higher raw material costs. Gross profit as a percentage of net revenues during the six months ended December 31, 2022 decreased on a year-over-year basis due to (i) a reduction in the Security division gross margins due to a decrease in margin from product sales driven by a less favorable product mix and increased component costs, (ii) a reduction in sales in the Healthcare division, which carries the highest gross margin of our three divisions, and (iii) an increase in sales in the Optoelectronics and Manufacturing division, which carries the lowest gross margin of our three divisions.
Operating Expenses
| | | | | | | | | | | | | | | | |
| | YTD Q2 | | % of | | YTD Q2 | | % of | | | | | |
| | Fiscal 2022 | | Net Revenues | | Fiscal 2023 | | Net Revenues | | $ Change | | % Change | |
Selling, general and administrative | | $ | 112.2 | | 20 | % | $ | 107.4 | | 77 | % | $ | (4.8) | | (4) | % |
Research and development | | | 29.8 | | 5 | | | 29.0 | | 21 | | | (0.8) | | (3) | |
Impairment, restructuring and other charges, net | | | 3.3 | | 1 | | | 3.5 | | 2 | | | 0.2 | | 4 | |
Total operating expenses | | $ | 145.3 | | 26 | % | $ | 139.9 | | 100 | % | $ | (5.4) | | (4) | % |
Selling, general and administrative. SG&A expense for the six months ended December 31, 2022 was $4.8 million lower than such expenses in the same prior-year period primarily due to a reduction in compensation, professional fees and favorable foreign exchange rates partially offset by a provision for bad debts compared to a bad debt recovery in the prior period.
Research and development. R&D expense during the six months ended December 31, 2022 decreased as compared to the same prior-year period primarily due to a decrease in outside services partially offset by increases in compensation and travel in our Security and Healthcare divisions.
Impairment, restructuring and other charges. During the six months ended December 31, 2022, impairment, restructuring and other charges primarily consisted of $2.9 million in legal charges primarily relating to government investigations and $0.5 million for employee terminations. During the six months ended December 31, 2021, impairment, restructuring and other charges consisted of $2.7 million for legal charges and $0.7 million in charges for employee terminations.
Interest and other expense, net. For the six months ended December 31, 2022, interest and other expense, net was $8.6 million as compared to $4.2 million in the same prior-year period. This increase was driven by higher average interest rates and higher average levels of borrowing under our credit facility during the six months ended December 31, 2022 in comparison with the levels of borrowing during the same period in the prior year. The 1.25% convertible notes that were previously outstanding during the six-month period ended December 31, 2021 were retired in September 2022 using borrowings from our credit facility which carries a higher interest rate.
Income taxes. For the six months ended December 31, 2022, we recognized a provision for income taxes of $7.6 million compared to $10.7 million for the comparable prior-year period. The effective tax rates for the six months ended December 31, 2021 and 2022 were 21.6% for both periods. During the six months ended December 31, 2022, we recognized discrete tax benefit of $0.5 million related to equity-based compensation under ASU 2016-09 and $0.4 million from changes in prior year estimates. During the six months ended December 31, 2021, we recognized a net discrete tax benefit of $1.8 million, which was comprised of $2.0 million related to equity-based compensation under ASU 2016-09 partially offset by a discrete tax expense for prior year tax estimates of $0.2 million.
Liquidity and Capital Resources
Our principal sources of liquidity are our cash and cash equivalents, cash generated from operations and our credit facilities. Cash and cash equivalents totaled $45.6 million at December 31, 2022, a decrease of $18.6 million, or 29.0%, from $64.2 million at June 30, 2022. We currently anticipate that our available funds, credit facilities and cash flow from operations will be sufficient to meet our operational cash needs for the next 12 months and the foreseeable future. In addition, we anticipate that cash generated from operations, without repatriating earnings from our non-U.S. subsidiaries, and our credit facilities will be sufficient to satisfy our obligations in the U.S.
We have a $750 million credit facility that is comprised of a $600 million revolving credit facility, which includes a $300 million sub-facility for letters of credit, and a $150 million term loan. As of December 31, 2022, there was $235.0 million outstanding under our revolving credit facility, $146.9 million outstanding under the term loan and $66.8 million of outstanding letters of credit. As of December 31, 2022, the total amount available under these credit facilities was $298.2 million.