Abstract: During fabrication of an insulated gate device, a drain-forming dopant having a relatively low diffusion coefficient is implanted along a substrate surface which overlaps the boundary between a to-be-formed vertical drain region and a to-be-formed adjacent channel region. During subsequent high temperature processing the low diffusion coefficient drain-forming dopant remains concentrated near the top surface of the substrate while other well-forming dopants, including an adjacent channel-forming dopant, which have relatively higher diffusion coefficients, diffuse to deeper regions of the substrate. The slow-diffusing drain-forming dopant retards lateral widening of the channel by the faster-diffusing channel-forming dopant just below the substrate surface to at least the depth of the channel inversion layer formed under the channel surface during device turn on.