A nitride-based semiconductor light-emitting device 100 includes: a GaN substrate 10 with an m -plane surface 12; a semiconductor multilayer structure 20 provided on the m -plane surface 12 of the GaN substrate 10; and an electrode 30 provided on the semiconductor multilayer structure 20. The electrode 30 includes an Mg layer 32 and an Ag layer 34 provided on the Mg layer 32. The Mg layer 32 is in contact with a surface of a p-type semiconductor region of the semiconductor multilayer structure 20.