We demonstrate the first tunable single wavelength quantum dot (QD) laser directly grown on Si. A simple, integrable architecture is implemented without involving re-growth steps or sub-wavelength grating lithography. 16 nm tuning range was achieved with over 45 dB SMSR and output powers exceeding 2.7 mW per tuning wavelength. The choice of QD gain material promotes high lasing efficiency in the presence of defects introduced by lattice-mismatched growth. Its insensitivity to defects and feedback also offers the prospect of utilizing the low-cost tunable laser structure in isolator-free PIC links on a Si substrate with high volume manufacturing.