Low-power high-speed optical receivers are required to meet the explosive growth in data communication systems. This paper presents a 26 GHz transimpedance amplifier (TIA) that employs a transformer-based regulated cascode (RGC) input stage which provides passive negative-feedback gain that enhances the effective transconductance of the TIA's input common-base transistor; reducing the input resistance and isolating the parasitic photodiode capacitance. This allows for considerable bandwidth extension without significant noise degradation or power consumption. Further bandwidth extension is achieved through series inductive peaking to isolate the photodetector capacitance from the TIA input. The optimum choice of series inductive peaking value and key transformer parameters for bandwidth extension and jitter minimization is analyzed. Fabricated in a 0.25-µm SiGe BiCMOS technology and tested with an on-chip 150 fF capacitor to emulate a photodiode, the TIA achieves a 53 dBΩ single-ended transimpedance gain with a 26 GHz bandwidth and 21.3 pA/ average input-referred noise current spectral density. Total chip power including output buffering is 28.2 mW from a 2.5 V supply, with the core TIA consuming 8.2 mW, and the chip area including pads is 960 µm x 780 µm.