Quantum mechanical electron tunneling has potential applications in both science and technology, such as flash memories in modern LSI technologies and electron transport chains in biosystems. Although it is known that one-dimensional quantum electron tunneling lacks temperature dependence, the behavior of electron tunneling between different dimensional systems is still an open question. Here, we investigated the electron tunneling between a two-dimensional electron gas (2DEG) and zero-dimensional Si quantum dots and discovered an unexpected temperature dependence: At high temperature, the gate voltage necessary for electron injection from 2DEG to Si quantum dots becomes markedly small. This unusual tunneling behavior was phenomenologically explained by considering the geometrical matching of wave functions between different dimensional systems. We assumed that electron tunneling would occur within a finite experimental measurement time. Then, the observed electron tunneling is explained only by the contributions of wave packets below the quantum dot with a finite lifetime rather than the ordinary thermal excited states of 2DEG.