Al0.45Ga0.55N/GaN solar-blind p-i-n photodiodes (PDs), fabricated by selective growth on SiO2 patterned n-GaN templates, are demonstrated in this paper. This selective-area-regrowth technique could lead to a reduction of tensile strain in the Al0.45Ga0.55 N/GaN epitaxial layers, thus alleviating the formation of cracks and reducing the dark current. The dry etching process was not required to expose the underlying layer before the formation of ohmic contact electrodes, simplifying the process tremendously. Compared with conventional solar-blind AlGaN/GaN p-i-n PDs, the proposed devices had lower dark current and higher detectivity. The experimental PDs exhibited a typical zero-bias peak responsivity of around 180 mA/W at 250 nm. This corresponded to quantum efficiency of around 90%. In addition, a nearly flat spectral response at the short-wavelength regions (220-270 nm) was observed. The typical ultraviolet-to-visible (250/450 nm) spectral rejection ratio at zero-bias was over four orders of magnitude. Typical specific detectivity at an incident wavelength of 250 nm was approximately 1.4×1013 cm Hz1/2W-1.