The cross-shell excited states of Si34 have been investigated via β decays of the 4- ground state and the 1+ isomeric state of Al34. Since the valence protons and valence neutrons occupy different major shells in the ground state as well as the intruder 1+ isomeric state of Al34, intruder levels of Si34 are populated via allowed β decays. Spin assignments to such intruder levels of Si34 were established through γ-γ angular correlation analysis for the negative-parity states with dominant configurations (νd3/2)-1⊗ - (νf7/2)1 as well as the positive-parity states with dominant configurations (νsd)-2⊗ - (νf7/2p3/2)2. The configurations of such intruder states play crucial roles in our understanding of the N=20 shell gap evolution. A configuration interaction model derived from the FSU Hamiltonian was utilized in order to interpret the intruder states in Si34. Shell model interaction derived from a more fundamental theory with the valence space in medium similarity renormalization group method was also employed to interpret the structure of Si34.