We characterized and studied tunable narrow-linewidth semiconductor lasers based on external cavity feedback and silicon-nitride micro-rings. Tuning of the driving current of the gain chip, voltages of the two micro ring thermoelectric electrodes, voltage of the phase saving thermoelectric electrodes, and temperature control of the semiconductor cooler, the C-band tunable output has been achieved in a side mode suppression ratio and output power larger than 52 dB and larger than 10 dBm, respectively. Further, white noise measurements of the narrow-linewidth semiconductor laser indicate a laser linewidth of 0.84 kHz, and the phase noise values at 0.01, 0.1 and 1 kHz are 581.04, 60.47 and 6.70 μrad/Hz^1/2, respectively. In the 1?20 GHz range, the relative intensity noise (RIN) of the laser is less than -156 dB/Hz. These excellent performance parameters of tunable narrow-linewidth semiconductor lasers suggest their application potential in optical fiber sensing, microwave photonics, coherent communication, and Doppler LiDAR.