Semiconducting materials are considered as excellent electrocatalysts for electrochemical water splitting; however, there is still a lack of relevant design and understanding of semiconducting composite electrodes. Here, a monolithic electrode composed of etched copper foam and p-n heterojunction (p-type Cu2O layer and n-type TiO2 nanodots with excellent hydrophilicity) is successfully prepared. This can reduce the electron transfer resistance, optimize water and H adsorption on catalyst surface and generate a space-charge region in phase interface, enhancing the local electrons density of Cu2O, which is proved by experimental results and density functional theory (DFT). Owing to the whole accelerated Volmer-Heyrovsky pathway, the as-prepared heterojunction electrode exhibits low onset potential (18 mV), high electrocatalytic activity (a potential of 114 mV at 10 mA cm(-2)) and long-term stability for hydrogen evolution reaction in alkaline media that is comparable to that of Pt, enabling the large scale fabrication.