Graphics-chip maker nVidia plans to restate two years of earnings and take non-cash charges of less than $150 million to correct accounting errors related to stock-based compensation expenses.

The company, which voluntarily launched a review of its stock options practices in June, found instances of "the use of incorrect measurement dates for certain option grants," it said Wednesday.

The revelation comes as a number of technology companies review how employee stock options have been dated back to a time when the stock had hit a low. The practice is unfair to shareholders and was made almost impossible to legally execute by Sarbanes-Oxley, and for good reason. Stock options were designed as a way for employees to share in the success of the company and give them an added incentive. But by back-dating the options, employees - often executives - were essentially given shares that were already valuable.

So far, probes at memory chip developer Rambus and security software vendor McAfee have led to the resignation or firing of executives.

nVidia plans to restate earnings for the fiscal years 2004 to 2006, as well as selected financial statements for earlier years, including the first quarter of its fiscal year 2007, which ended April 30, 2006. The company said the restatements will decrease its reported net profit for the periods in question, or increase losses as the case may be, but it does not expect the restatements to impact revenue or its cash position for any period.

nVidia auditors have not yet completed their review of the findings in the options probe.