The present invention provides a submount that allows a semiconductor light-emitting element to be attached with a high bonding strength.A submount 3 is equipped with a substrate 3 and a solder layer 8 formed on a primary surface 4f of the substrate 4. The density of the solder layer 8 is at least 50% and no more than 99.9% of the theoretical density of the material used in the solder layer 8. The solder layer 8 contains at least one of the following list: gold-tin alloy; silver-tin alloy; and lead-tin alloy. The solder layer 8 before it is melted is formed on the substrate 4 and includes an Ag film 8b and an Sn film 8a formed on the Ag film 8b. The submount 3 further includes an Au film 6 formed between the substrate 4 and the solder layer 8.