Strongly electron-deficient pi-conjugated systems are key building units for semiconducting polymers that are used in organic electronic devices, such as organic photovoltaic (OPV) cells. Here, we designed and synthesized a naphthobispyrazine derivative bearing four ester groups (eNPz) as a new electron-deficient building unit and three eNPz-based semiconducting polymers with different donor units, that is, bithiophene (PeNPz2T), terthiophene (PeNPz3T), and quaterthiophene (PeNPz4T). These new polymers have relatively deep lowest unoccupied molecular orbital (LUMO) energy levels of around -3.5 eV, along with narrow optical band gaps of around 1.5 eV. The LUMO energy levels and the optical band gaps are significantly deeper and narrower than those of a polymer based on alkylated naphthobispyrazine. The results indicate that eNPz has a strong electron deficiency. The polymers show reasonably high power conversion efficiency of more than 6% in OPV cells in combination with a fullerene derivative. This study demonstrates that eNPz can be a useful building unit for high-performance semiconducting polymers.