Characteristics of high-speed bipolar junction transistors are considered regarding their application to chaotic HF and UHF Colpitts oscillators. Chaotic domains are investigated in the parameter (current gain betaversus threshold frequency f(T)) plane. The highest achievable fundamental frequency f* of chaotic oscillations is found to be 10 times less than f(T). The influence of the parasitic collector-base and emitter-base capacitances is analysed.