Geometrical effects on the forward characteristics of high-power bipolar junction transistors are studied. An implantation-free area optimized junction termination is implemented in order to have a stable breakdown voltage. The effect of varying the emitter-base geometry, i.e., the emitter width (W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</sub> ), the base width (W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> ), emitter contact-emitter edge distance (W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> ), and base contact-emitter edge (W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> ) on the on-state characteristics is studied in the different emitter cell geometries. The emitter size effect shows the highest influence on the current gain (fi). It shows a significant effect on the fi (single finger design, about 61%; square cell geometry, about 98%; hexagon cell geometry, about 90%). The base size effect also shows a significant improvement on the fi of about 23% at a given W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</sub> .