Layered semiconductor gallium selenide (GaSe) is considered a potential candidate for optoelectronic applications because of its direct band gap. Monocrystalline material is, however, a prerequisite to fully exploit these properties in devices, where one-dimensional nano-objects could be considered as a model system. As a consequence of their large surface-to-volume ratio, nano-objects such as nanoribbons are interesting for photodetection applications. Here, we report the vapor–liquid–solid growth of GaSe nanoribbons by MOCVD on 300 mm silicon substrates. A growth model is proposed on the basis of a comprehensive study of the impact of the growth parameters on the nanoribbon morphology. The nanoribbon microstructure is investigated by HR-STEM and Raman spectroscopy characterizations. HR-STEM and TEM cross-sectional observations coupled with EDX analyses reveal a monocrystalline nanoribbon core covered with a native gallium-oxide shell. Test devices are made by contacting individual nanoribbon. The current versus voltage (I–V) characteristic obtained over a range of temperature (−50 to 100 °C) in the dark and under white light illumination is fitted on the basis of a back-to-back Schottky diode model. A stable and repeatable dynamic photoresponse is measured from the GaSe nanoribbons, with an ION/IOFF ratio of 17 at room temperature.