Abstract Metal-assisted chemical etching (MacEtch) of silicon shows reliable vertical anisotropic wet etching only in single-crystal silicon, which limits its applications to a small number of devices. This work extends the capabilities of MacEtch to polysilicon which has potential to enable high-volume and cost-sensitive applications such as optical metasurfaces, anodes for high capacity and flexible batteries, electrostatic supercapacitors, sensors, nanofluidic deterministic lateral displacement devices, etc. This work presents a MacEtch of polysilicon that produces nanostructure arrays with sub-50 nm resolution and anisotropic profile. The three demonstrated structures are pillars of 5:1 aspect ratio and 50 nm spacing for comparison to single crystal silicon MacEtch literature, pillars of 30 nm spacing, and a diamond pillar array with sharp corners to establish resolution limits of polysilicon MacEtch.