A high-voltage MOS transistor having: a first region of a first conductivity type; a source region of the second conductivity type, which is introduced into the first region; a drain region of the second conductivity type, which is introduced into the first region; a channel region on the upper side of the first region, between the source region and the drain region; a field-oxide region in the drain region, between the source region and the drain region; a gate-oxide region over the channel region and between the edge of the drain region and the field-oxide region; a magnetoresistor region between the source region and the drain region, over the gate-oxide region and over at least a part of the field-oxide region; the drain region having a drain-terminal region and a drain-extension region and the doping profile of the drain-extension region is designed so that an avalanche breakdown occurs between the source region and the drain region, in a breakdown region that is on the edge of the drain-extension region and is not situated at the upper surface. Also it describes corresponding manufacturing methods.