Pricing pressure for its data storage equipment contributed to Qualstar Corp.’s declining revenue in the fourth quarter, which drop its share price more than 12 percent Friday.

The Simi Valley manufacturer reported a net loss of $407,000 (-20 cents a share) on revenue of $2.2 million in the quarter ended Dec. 31. That compares to a net loss of $429,000 (-21 cents) on revenue of $2.6 million in the same period a year earlier.

Sales of data storage products decreased by 38 percent to $800,000 in the fourth quarter compared to sales of $1.3 million in the same period from a year earlier. In contrast, sales of the company’s power supply products increased 8 percent to $1.4 million for the quarter.

Chief Executive Steve Bronson said that competition in the in the data storage industry has created pressure on the company to maintain its market share.

“However, investments we have made in our cost structure are beginning to emerge as we were able to keep our expenses in line with the decline in sales,” Bronson said in a prepared statement.

Earnings were released late Thursday. Shares closed Friday down $1.03, or 12.4 percent, to $7.29 on the Nasdaq.