A new measurement method for curvature distribution of warped SiO_2-GaAs substrate using differential diffraction angles with respect to a standard rocking curve for flat substrate is presented. These rocking curves are measured by x-ray double crystal method for each reflection from the points which are selected at regular intervals on the specimen by moving the slit placed in front of the specimen. The measurement method is applied at room temperature to three cases of SiO_2-GaAs substrate whose SiO_2 film has been deposited uniformly by CVD at 350℃. These three cases are: i) SiO_2 film deposited on the whole substrate, ii) SiO_2 film partially removed, iii) SiO_2 film completely removed. The results of measurements reveal the following facts. SiO_2-GaAs substrate is warped uniformly independent of the distribution of the lattice defects in the substrate due to the difference of thermal expansion coefficient between SiO_2 film and GaAs crystal. Namely the SiO_2 film on the GaAs crystal is in a state of compression. There is an appreciable difference of the curvature between those for SiO_2 film deposited area and SiO_2 film removed area.
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