Recently, hydrovoltaic technology emerged as a novel renewable energy harvesting method, which dramatically extends the capability to harvest water energy. However, the urgent issue restricting its device performance is poor carrier transport properties of the solid surface if large charged interface is considered simultaneously. Herein, a hydrovoltaic device based on silicon nanowire arrays (SiNWs), which provide large charged surface/volume ratio and excellent carrier transport properties, yields sustained electricity by a carrier concentration gradient induced by evaporation‐induced water flow inside nanochannels. The device can yield direct current with a short‐circuit current density of over 55 μA cm−2, which is three orders larger than a previously reported analogous device (approximately 40 nA cm−2). Moreover, it exhibits a constant output power density of over 6 μW cm−2 and an open‐circuit voltage of up to 400 mV. Our finding may pave a way for developing energy‐harvesting devices from ubiquitous evaporation‐driven internal water flow in nature with semiconductor material of silicon.

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