if the depletion width becomes wide enough, then electrons appear in a very thin layer at the semiconductor-oxide interface, called an inversion layer because they are oppositely charged to the holes that prevail in a p-type material. when an inversion layer forms, the depletion width ceases to expand with increase in gate charge "q". in this case, neutrality is achieved by attracting more electrons into the inversion layer. in the mosfet, this inversion layer is referred to as the channel.