Semiconductor manufacturing processes are characterized by complexity and long lead times, making efficient production planning crucial. Existing methods using fixed and proportional lead times fail to fully account for production line variability. This study proposes an optimization model for semiconductor production planning that incorporates production line availability. The model addresses this issue by distinguishing between available and non-available work-in-process (WIP). The proposed model was tested using simulation, which confirmed its ability to reduce the discrepancy between planned and actual throughput, improving production plan feasibility and achieving high order fulfillment rates. Moreover, it maintains short lead times, reduces WIP variance, and supports high production volumes. This helps companies manage production lines more efficiently, leading to enhanced productivity and profitability.