This paper proposes a new linear laser phase-locked thermal imaging technology for surface crack instantaneous imaging detection of semiconductor chips. The technical system consists of a linear scanning laser source, a high-speed infrared camera, and a control computer. The surface of the target chip is scanned by a linear laser beam and the thermal wave propagation is measured by an infrared camera. A new visualization algorithm without baseline crack is proposed. Because cracks can cause thermal wave blocking, they can be visualized and diagnosed automatically, which is independent of baseline data obtained from the original state of the target chip. The microcracks of the chips generated in the manufacturing process are studied. The experiments demonstrate that the visualization of cracks with a width of tens of micrometers can be realized by the laser phase-locked thermal imaging technology.