A power semiconductor device having a current detecting function comprising a detection part that includes the elements of a better reach-through withstand voltage capability than those of a principal current part. The power semiconductor device comprises such elements as DMOS, IGBT or BPT cells. One area of the device acts as the detection part and another as the principal current part. The detection part and the principal current part share as their common electrode a high density substrate having a low density layer of a first conductivity type. The surface of the low density layer carries a principal and a subordinate well region of a second conductivity type each. The surface of the principal well region bears a surface electrode region of the first conductivity type acting as the other electrode of the principal current part; the surface of the subordinate well region carries a surface electrode region of the first conductivity type acting as the other electrode of the detection part. The subordinate well region is made shallower than the principal well region illustratively by use of a mask having narrower apertures through which to form the former region. This causes a reach-through to occur in the principal current part with its well region having a shorter distance to the high density substrate, and not in the detection part with its well region having a longer distance to the substrate.