This paper presents compact D-band amplifiers in 55 nm SiGe BiCMOS technology. Device models and design tools are first validated with measurements on elementary components above 100 GHz. Then, amplifiers are designed leveraging lumped components in matching networks for minimum area occupation. A differential topology is developed for robustness against parasitic effects of the non-ideal ground, a key issue with lumped components at high frequency. Experimental results are in very good agreement with simulations. The 1-stage amplifier reaches 8 dB gain at 156 GHz and 17.8 GHz bandwidth in 0.026 mm2 silicon area. The 2-stage amplifier displays 17.4 dB gain at 157 GHz with 42.7 GHz bandwidth in 0.048 mm2. Compared to previously reported SiGe amplifiers in similar frequency range, more than 2x core area reduction is demonstrated at comparable gain-bandwidth product.