in an n-type semiconductor number of free electron is more than number of holes .why it doesn't have net -ve charge?

Dear Student,

The extrinsic semiconductor is electrically neutral i.e. neither n-type semiconductor has negative charge nor p-type semiconductor carries positive charge.

They have same number of protons as the number of electrons so they are electrically neutral. Free electrons or holes in extrinsic semiconductors is due to the lack of electrons to make bonds.