PURPOSE: To obtain a semiconductor device capable of easily obtaining diffusion depth, managing wafer process, and realizing a high quality wafer, and a diffusion depth measuring method using the semiconductor device.

CONSTITUTION: Along one direction of a diffusion region 2a to be measured which is formed on a wafer 1, a plurality of comparison diffusion regions 2b, 2c, 2d which are different in the intervals from the region 2a are formed, a drain electrode 4 is formed on the region 2a, and source electrodes 3b, 3c, 3d are formed on the regions 2b, 2c, 2d. A gate electrode 5 is formed between the drain electrode and the source electrodes. Whether an FET structure is formed is examined about each of the pairs of the diffusion region 2a to be measured and the comparison diffusion regions 2b, 2c, 2d. About the pair in which the FET structure is formed, the interval between the source electrode and the drain electrode is measured, and the diffusion depth is obtained by multiplying the minimum value by a specified coefficient.