Rapid scaling of transistor dimensions has intensified power-consumption challenges in modern microelectronics. The subthreshold slope (SS) quantifies the gate-voltage change required for a decade change in drain current and fundamentally limits both static and dynamic power dissipation. In conventional semiconductor transistors, the SS is constrained by the Boltzmann limit of about 60 mV/dec at room temperature. It is of great importance to explore materials and device strategies to surmount this thermodynamic limit. In this perspective, we first briefly outline the fundamental law that governs the 60 mV/dec switching limit in traditional metal-oxide-semiconductor field effect transistors (MOSFETs). Then we critically review emerging approaches that have demonstrated potential to surpass this 60  mV/dec limit, including device architectures like tunnel FETs (TFETs), negative-capacitance FETs (NCFETs) and nano-electro-mechanical (NEM) switches. Furthermore, we discuss the operational principle of a biological switch—voltage-sensitive ion channels, which manifest evident sub-60 mV/dec switching behaviors. Inspired by such a biological phenomenon, we develop a unified, multi-charge based interpretation to explain the steep SS performance in these non-conventional electrical, mechanical and biological switches. This perspective would suggest potential paradigm-shift approaches to realize ultra-steep-slope and low-power electronics.