Sales in the Data Center Computing market decreased $19.3 million, or 22.0%, to $68.3 million for the three months ended September 30, 2023 and $45.9 million, or 19.7%, to $187.0 million for the nine months ended September 30, 2023 as compared to the same periods in the prior year. The decrease in Data Center Computing market sales was due to the cyclical downturn in the data center server and storage market, partially offset by increased demand for advanced computing applications by some customers.
Sales in the Telecom and Networking market decreased $1.1 million, or 2.6%, to $41.4 million for the three months ended September 30, 2023 and increased $29.3 million, or 25.3%, to $145.3 million for the nine months ended September 30, 2023 as compared to the same periods in the prior year. The decrease in sales during the three month period was due to slowing market demand. The increase in sales for the nine month period was primarily due to substantially improved material availability, allowing us to largely fulfill outstanding demand from the prior year.
GROSS PROFIT
For the three months ended September 30, 2023, gross profit decreased $43.9 million to $147.3 million, or 35.9% of revenue, as compared to $191.2 million, or 37.0% of revenue, in the same period in the prior year. For the nine months ended September 30, 2023, gross profit decreased $48.2 million to $449.5 million, or 35.9% of revenue, as compared to $497.7 million, or 36.7% of revenue, in the same period in the prior year.
The decrease in gross profit as a percentage of revenue for the three and nine months ended September 30, 2023 was largely due to the decline in sales, unfavorable product mix, and higher operating costs based on investments made in 2022, partially offset by lower premiums and related recoveries for securing critical parts.
OPERATING EXPENSES
Research and Development
We perform research and development (“R&D”) to develop new or emerging applications, technological advances to provide higher performance, lower cost, or other attributes that we may expect to advance our customers’ products. We believe that continued development of technological applications, as well as enhancements to existing products and related software to support customer requirements, are critical for us to compete in the markets we serve. Accordingly, we devote significant personnel and financial resources to the development of new products and the enhancement of existing products, and we expect these investments to continue.
R&D expenses increased $0.6 million to $50.4 million for the three months ended September 30, 2023 and increased $12.0 million to $153.4 million for the nine months ended September 30, 2023 as compared to the same periods in the prior year. The increase in R&D expense for the three months ended September 30, 2023 was primarily driven by increased headcount and compensation costs. The increase for the nine months ended September 30, 2023 was primarily driven by increased headcount and compensation costs of $8.3 million, which was partially due to the SL Power acquisition. In addition, during the nine months ended September 2023, we incurred $3.8 million in higher program and material costs as we invested in new programs to maintain and increase our technological leadership and provide solutions to our customers’ evolving needs.
Selling, General, and Administrative
Our selling expenses support domestic and international sales and marketing activities that include personnel, trade shows, advertising, third-party sales representative commissions, and other selling and marketing activities. Our general and administrative expenses support our worldwide corporate, legal, tax, financial, governance, administrative, information systems, corporate development, and human resource functions.
Selling, general and administrative (“SG&A”) expenses decreased $1.6 million to $55.1 million for the three months ended September 30, 2023 and increased $5.0 million to $166.1 million for the nine months ended September 30, 2023 as compared to the same periods in the prior year. The decrease in SG&A during the three month period was primarily due to lower employee variable compensation expense, partially offset by higher stock-based compensation cost. The increase in SG&A for the nine month period was primarily related to higher stock-based compensation cost and the addition of SL Power, partially offset by lower employee variable compensation expense.