We have proposed a tunable laser with silica-waveguide ring resonators. In this tunable laser, a semiconductor optical amplifier was passively aligned and mounted onto a silica-waveguide substrate. The ring resonators can be tuned by controlling their temperatures using the thermo optic heaters formed on them, and there are no mechanically moving parts. Thus, they are sufficiently stable and reliable for practical use. Our tunable laser exhibits a high fiber-output power of more than 15dBm and a wide tunable range of 60nm (L-band, 50GHz spacing, 147 channels). Moreover, a tunable laser with a much wider tunable range of 96nm using 100-GHz-FSR ring resonators is also reported.