a matrix of columns and rows of conductors with transistors located at the intersection thereof on a semiconductor chip is formed utilizing the washed emitter process which locates the ohmic contact windows close to the pn junction so that a small size piece of free metal , i . e ., not connected to any other conductor , may be located within a shot distance , i . e ., one micron or less , to the pn junction selected to be fused during the programming of a read only memory . the small size of the free metal as near as possible to this pn junction minimizes heat losses , reduces power consumption and reduces programming errors normally incurred in the programming of read only memories .