Open the door in the middle of the cycle to see if the water level seems too high. It should not be as high as the door hinge when full. If it seems too high, you will have to check the float valve in the front left corner inside the dishwasher. It may be stuck thus overfilling tub. Pay attention to the position of parts and remove the cover, take it apart, and use a small brush,q-tip etc to clean it. Make sure it moves up and down freely before replacing everything. Other possible but less likely causes are leaking door gasket, or plugged drain (or kinked drain hose) preventing water from being pumped out completely.
Ronald Bowman, February 2007