It is well known that neat PLA is not inclined to crystallization, which results in inferior mechanical properties compared to commodity plastics like polyethylene. To empower PLA for commercial applications, the overall degree of crystallinity has to be increased. In this study, the crystallinity of PLA-compounds was influenced via (a) processing conditions and (b) addition of fillers. Mold temperatures for conventional injection molding on PLA are generally set in the range of 10 °C to 25 °C while the crystallization temperature lies well over 100 °C. In general, this leads to amorphous parts. Due to this fact, tempering is often used as a second manufacturing step in order to generate crystallinity. Another well-known approach to promote crystallization in PLA is the addition of fillers as nuclei. In this work, an in-mold-tempering approach via Rapid-Heat-Cycle-Molding was designed and conducted to enable single-step manufacturing of crystalline PLA parts. To enable crystallization, the mold temperature was elevated above the crystallization temperature before start of injection, held for prolonged times (time for in-mold-tempering) and rapidly cooled down to conventional mold temperatures again. In order to evaluate the effectiveness of the in-mold-tempering approach, different PLA compounds (with varied amounts of silica and talcum) were tested in addition to neat PLA, followed by measurements of the degree of crystallinity via differential scanning calorimetry.