A method for efficiently producing a plate-like nitride semiconductor crystal having the desired principal plane in a simple method is provided. A raw material gas is fed to a seed crystal in which a ratio (L/W) of length L in a longitudinal direction and maximum width W, of a plane of projection obtained by projecting a crystal growth face on the seed crystal in a growth direction is from 2 to 400, and the maximum width W is 5 mm or less, thereby growing a plate-like semiconductor crystal on the seed crystal.