A semiconductor device may include a substrate and an inverted T channel on the substrate and including a superlattice. The superlattice may include stacked groups of layers, with each group of layers including stacked base semiconductor monolayers defining a base semiconductor portion, and at least one non-semiconductor monolayer constrained within a crystal lattice of adjacent base semiconductor portions. The semiconductor device may further include source and drain regions on opposing ends of the inverted T channel, and a gate overlying the inverted T channel between the source and drain regions.