The transmission of a Ti:sapphire laser beam (c. w. and fs pulsed operation at 800 nm) through a 10 µm thin oxidized silicon membrane at 45° angle of incidence at first increases with the incident laser power, then shows a maximum, and finally decreases considerably. This nonlinear transmission behavior is the same for c.w. and pulsed laser operation and mainly attributed to free charge carrier absorption in Si.