three months ended September 30, 2019 and 2020, respectively. Selling, general and administrative expenses were unchanged at $5.5 million in the six months ended September 30, 2019 and in the six months ended September 30, 2020. Decreases in independent sales representative commissions of $287,000 and $88,000 in travel expenses were primarily offset by increases in payroll expenses, professional fees and stock-based compensation expense. Selling, general and administrative expenses included stock-based compensation expense of $390,000 and $470,000 for the six months ended September 30, 2019 and 2020, respectively.
Interest Income, Net. Interest and other income, net decreased 107.6% from income of $210,000 in the three months ended September 30, 2019 to an expense of $16,000 in the three months ended September 30, 2020. Interest income decreased by $136,000 primarily due to lower interest rates received on our cash and short-term and long-term investments. Foreign exchange losses were $5,000 for the three months ended September 30, 2019 compared to $96,000 for the three months ended September 30, 2020. The exchange losses in each period were related to our Taiwan branch operations and our operations in Israel. Interest and other income, net decreased 74.8% from income of $357,000 in the six months ended September 30, 2019 to $90,000 in the six months ended September 30, 2020. Interest income decreased by $226,000 primarily due to lower interest rates received on our cash and short-term and long-term investments. We had a foreign exchange loss of $63,000 for the six months ended September 30, 2019 compared to $104,000 for the six months ended September 30, 2020. The exchange losses in each period were related to our Taiwan branch operations and our operations in Israel.
Provision for Income Taxes. The provision for income taxes increased 12.7% from $55,000 in the three months ended September 30, 2019 to $62,000 in the three months ended September 30, 2020 and increased 460.2% from $98,000 in the six months ended September 30, 2019 to $549,000 in the six months ended September 30, 2020. This change for the six month period was primarily due to the settlement of an income tax audit in Israel during the quarter ended June 30, 2020 for fiscal years 2016 through fiscal 2019 which resulted in a discrete tax provision of $479,000, and to a lesser extent due to fluctuations in the relative mix of income among our operating jurisdictions.
Net Loss. Net loss was $1.8 million in the three months ended September 30, 2019 compared $5.2 million in the three months ended September 30, 2020 and was $1.9 million in the six months ended September 30, 2019 compared to $11.3 million in the six months ended September 30, 2020. These fluctuations were primarily due to the changes in net revenues, gross profit and operating expenses discussed above.
Liquidity and Capital Resources
As of September 30, 2020, our principal sources of liquidity were cash, cash equivalents and short-term investments of $56.1 million compared to $66.6 million as of March 31, 2020.
Net cash used in operating activities was $8.3 million for the six months ended September 30, 2020 compared to $1.1 million for the six months ended September 30, 2019. The primary uses of cash in the six months ended September 30, 2020 was the net loss of $11.3 million and a reduction in accrued expenses and other liabilities of $1.9 million. The reduction in accrued expenses and other liabilities was primarily related to the payment of fiscal 2020 year-end accruals for purchased intellectual property. Primary sources of cash in the six months ended September 30, 2020 were a reduction in accounts receivable of $2.1 million and non-cash items including stock-based compensation of $1.4 million and depreciation and amortization expenses of $707,000. The decrease in accounts receivable was primarily due to the decrease in shipments in the quarter ended September 30, 2020 compared to the quarter ended March 31, 2020.
The primary uses of cash in the six months ended September 30, 2019 was the net loss of $1.9 million, a reduction in accrued expenses and other liabilities of $1.4 million and a lesser amount related to an increase in prepaid expenses and other assets. The reduction in accrued expenses and other liabilities was primarily related to the payment of fiscal 2019 year-end compensation related accruals. Primary sources of cash in the six months ended September 30, 2019 were non-cash items including stock-based compensation of $1.3 million and depreciation and amortization expenses of $727,000.
Net cash used in investing activities was $1.7 million in the six months ended September 30, 2020 compared to net cash provided by investing activities of $1.2 million in the six months ended September 30, 2019.