SERVICE ENGINE LIGHT COMES ON

I HAVE A 95 CHEVY FULLSIZE. WHEN I START THE TRUCK UP, DRIVE IT FOR ABOUT 10 MINUTES, THE ENGINE SERVICE LIGHT COMES ON. WHEN I TURN THE TRUCK OFF AND LET IT SIT FOR AWHILE, THE LIGHT WILL NOT COME ON WHEN I RESTART THE TRUCK. HOWEVER ITLL COME ON AGAIN THE SAME WAY AFTER TEN MINUTES OF DRIVING IT. WHAT COULD IT BE?? O2 SENSOR OR SOMETHING ELSE?? LET ME KNOW.