Cost of revenue was $16 thousand in the three months ended March 31, 2023, compared with $23 thousand in the same period of 2022. Cost of revenue resulted from the sale of the OTFT backplanes and materials described above.
Other operating income
Other operating income was $269 thousand in the three months ended March 31, 2023, compared to $284 thousand in the same period of 2022, a decrease of $15 thousand, or 5.3%. The decrease resulted primarily from an increase of $53 thousand recorded for a research grant, offset by a decrease of $68 thousand in research and development tax credits compared to the prior period of 2022.
Operating expenses
Operating expenses were $2.8 million for the three months ended March 31, 2023, compared to $2.7 million in the same period of 2022, an increase of $0.1 million, or 4.6%.
Research and development expenses are incurred for the development of TRUFLEX® inks to make OTFT circuits and consists primarily of payroll and technical development costs. The research and development expenses represents 45% and 54% of the total operating expenses for the three months ended March 31, 2023 and 2022, respectively. For the three months ended March 31, 2023 research and development expenses decreased to $1.3 million from $1.5 million in the prior year period. The decrease of $0.2 million is primarily due to the reduction of personnel and a reduction in professional service fees.
Selling, general and administrative expenses consist primarily of payroll, and professional services such as accounting, legal services and investor relations, These expenses represent 51% and 46% of our total operating expenses for the three months ended March 31, 2023 and 2022, respectively. Selling, general and administrative expenses of $1.4 million for the quarter, increased by $0.2 million from the prior year period, primarily as a result of increased investor relations expenses.
Losses on foreign currency transactions related to operating expense were $0.1 million for the three months ended March 31, 2023.
Non-Operating income/(expense)
Gains on foreign currency transactions related to intercompany loans were $0.5 million for the three months ended March 31, 2023 compared to the losses of $0.4 million for the three months ended March 31, 2022. The increase of $0.9 million is related to the favorable changes in the exchange rates.
Liquidity and Capital Resources
To date, we have funded our liquidity and capital requirements primarily with proceeds from the private sale of our equity and debt securities and borrowing against our research and development credits. As of March 31, 2023, our cash and cash equivalents were $1.7 million compared with $4.2 million as of December 31, 2022. The decrease of $2.5 million is all related the cash used in operating activities.
We believe that our existing cash as of March 31, 2023 will be sufficient to fund our operations through the end of May 2023 if we continue to spend to our forecast, and that we will require additional capital funding to continue our operations and research and development activity thereafter.
Our future results are subject to substantial risks and uncertainties. We have operated at a loss for our entire history and anticipate that losses will continue over the coming year. We will need to obtain additional funds to satisfy our operational needs and to fund our sales and marketing efforts, research and development expenditures, and business development activities. Our future liquidity and working capital requirements will depend on many factors including our ability to generate revenue from product sales, the timing and extent of spending to support our sales and marketing, product development and research and development efforts, our entry into one or more material agreements containing significant performance obligations and our needs for working capital to support our business operations. Until such time, if ever, as we can generate sufficient cash through revenue, we expect to finance our working capital requirements through a combination of equity