A detailed experimental study has been made of the issues related to base dopant activation and mesa isolation in collector-up SiGe HBTs. It is concluded that to avoid excessive emitter-base diode leakage: (i) the metallurgic emitter-base junction should be moved away from the trenched p(+) base doping peak, and (ii) the base contact implant should not be placed in the high n-doped emitter substrate. Both recommendations can be followed by applying an implanted pedestal emitter. To furthermore avoid TED, the base contact implantation is activated by laser annealing. To achieve a good quality collector-base diode, a p(-)nn(+) collector profile is introduced. As a result, the transistor profile is a stack of several doped Si and SiGe layers. This stack is grown by A-P/LPCVD dichlorosilane based epitaxy, which was optimised to suppress autodoping and to achieve sharp transitions. Hence the 1150 degreesC prebake was performed at low pressure and high flow, and followed by a 10 nm undoped Si deposition at 700 degreesC. Moreover, 5 nm undoped Si layers were inserted for dopant decoupling. The effect of the p(-) layer in the collector on the device behaviour was analysed by device simulations. It was found that this p(-) layer does not significantly affect the DC and high-frequency performance of the device.