With the aim of producing polylactide fibers consisting of highly oriented stereo-complex (SC) crystals, high-speed bicomponent melt spinning of the islands-in-the-sea (I/S) fibers consisting of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) as the sea and island components, respectively, was performed. For comparison, bicomponent spinning of the core-sheath (C/S) fibers consisting of PLLA and PDLA as the sheath and core components was also carried out. Structure analysis of the C/S fibers revealed that the orientation-induced crystallization of the higher molecular weight component, PLLA, started from the take-up velocity of around 4 or 5 km/min, whereas there was a significant orientation relaxation of the lower molecular weight component, PDLA, with the further increase of take-up velocity up to 10 km/min. After the on-set of orientation-induced crystallization, development of only homo-crystals was confirmed through the wide-angle X-ray scattering analysis. On the other hand, through the differential scanning calorimetry (DSC) of the I/S fibers, along with the melting peak of homo-crystals, distinct melting peak of the SC crystals was observed. This result suggested the mutual diffusion of PLLA and PDLA molecules during the DSC analysis. Based on these results, post-annealing of the as-spun fibers was attempted at the temperatures of 120 and 190 °C, considering the melting temperatures of the homo and SC crystal of 160 and 220 °C. It was found that the high-speed spun I/S fibers could maintain their shapes after the annealing at 190 °C under constant length condition if the orientation-induced crystallization proceeded in the spinning process. After the annealing, fibers consisting of a large amount of highly oriented SC crystals was formed successfully, indicating that the diameter of the island fibers was small enough for the efficient mutual diffusion of the PLLA and PDLA molecules in the fiber cross-section.