A monolithic electronic device includes a substrate, a semi-insulating, piezoelectric Group III-nitride epitaxial layer formed on the substrate, a pair of input and output interdigital transducers forming a surface acoustic wave device on the epitaxial layer and at least one electronic device (such as a HEMT, MESFET, JFET, MOSFET, photodiode, LED or the like) formed on the substrate. Isolation means are disclosed to electrically and acoustically isolate the electronic device from the SAW device and vice versa. In some embodiments, a trench is formed between the SAW device and the electronic device. Ion implantation is also disclosed to form a semi-insulating Group III-nitride epitaxial layer on which the SAW device may be fabricated. Absorbing and/or reflecting elements adjacent the interdigital transducers reduce unwanted reflections that may interfere with the operation of the SAW device.