Structure devpelopment in the continuous laser-drawing process of poly(ethylene terephthalate) fibers was investigated with a time resolution of 0.2 ms by real time synchrotron X-ray diffraction and fiber temperature measurements. The (001') and (003') reflections of a quasi-smectic fibrillar structure were observed from 0.16 ms after necking, and the reflection intensity reached a maximum at around 0.3 ms after necking, when the elastic energy stored at the necking had been released. The d-spacing of the (001') reflection decreased with increasing time, and the quasi-smectic fibrillar structure had a length of 70 nm and a radius of 7.0 nm. The crystallization induction time and crystallization rate were 0.3 ms and 1100 s(-1) based on the fiber temperature profile and 0.6 ms and 1400 s(-1) based on the equatorial reflection intensity profiles. In the azimuthal intensity profile under the 2010 arrangement, a single meridional peak of the (003') plane was observed, and it is considered that the quasi-smectic fibrillar structure oriented uniaxially along the fiber axis with an orientation factor of 0.986.