A monolithic integrated circuit (IC) chip containing a plurality of transistors, including: a substrate; a first transistor on the substrate; and a second transistor integrally formed on the substrate with the first transistor, the second transistor having a different structure than the first transistor, wherein the first transistor includes a first material system and the second transistor includes a second material system different from the first material system. The monolithic IC chip may further include a third transistor integrally formed on the substrate with the first and second transistors. The first transistor may include gallium nitride (GaN) and the second and third transistors may include silicon carbide (SiC).