Internal stress in a-Si:H films prepared by plasma chemical vapor deposition was studied in connection with optical degradation or Staebler-Wronski effect (SWE). It was found that the stress increased with increasing discharge power density (0.03 ∼ 1.5 W/cm2) of silane, accompanied by increase in the introduction rate of SWE. These results imply that highly decomposed radical species due to high discharge power density dominate the surface reaction. Consequently, larger stress and larger introduction rate of SWE are brought about in the films. The stress also slightly increased at lower power density (< 0.03 W/cm2), suggesting that neutral silane molecules take part in the reaction at these power density.