Former Enron Corp. Chief Executive Jeffrey Skilling ended lengthy testimony in his federal fraud trial Thursday by denying a new government accusation — that he may have cheated on his taxes.

Skilling calmly said he didn’t recall backdating a $10,000 gift check to an ex-girlfriend to avoid paying taxes on it in 1998, and he told jurors that he has heard nothing from the Internal Revenue Service despite repeated reviews of his tax returns.