In this short note we discuss briefly several key issues in processor design using LSI GaAs integrated circuits, as well as the major bottlenecks encountered, which impair and limit the performance of this very high speed technology. We draw some conclusions about the limited usefulness of the LSI blocks currently available for system partitioning, and their pros and cons. The discussion derives from analysis and from a GaAs version of a Silicon 8/16 bit bipolar microprocessor (called CPA). Both versions have been implemented in our laboratory for demonstration purposes. These processors emulate the complete i8085 instruction set.