A transistor device includes a semiconductor substrate and a gate structure formed over the substrate. Forming the gate structure may include steps of forming a multi-layer dielectric stack over the substrate, performing an anisotropic dry etch of the multi-layer dielectric stack to form a gate channel, forming a conformal dielectric layer over the substrate, performing an anisotropic dry etch of the conformal dielectric layer to form dielectric sidewalls in the gate channel, etching portions of dielectric layers in a gate channel region, and forming gate metal in the gate channel region. Dielectric spacers may be similarly formed in a field plate channel prior to formation of a field plate of the transistor. By forming dielectric spacers in the gate channel, the length of the gate structure can be advantageously decreased.