Abstract: The base layer of a power permeable base transistor is formed as comb structures with grating teeth of the combs extending into active regions of semiconductor material. Extended active regions are separated by inactive regions over which collector contacts extend. Large devices have digitated base layers. The comb structures are fabricated by sputtering a uniform layer of tungsten and forming a nickel mask over the tungsten by both X-ray and photolithography techniques. The tungsten exposed by the nickel mask is then etched to leave the comb structures.