In this paper, we present a new method of determination of the gap state distribution in a-Si :H—the internal photoemission transient current temperature spectroscopy(IPETCTS). By this method, we suceeded in determining the GDOS distribution N(E) in a GD a-Si:H film. The result agrees in shape with that obtain ed from the typical field effect measurement, while the magnitude of the gap state density.obtained from the IPBTCTS is smaller by one to two orders than that from field effect measurement.