As we know, an n-type semiconductor has large number of electrons but it is still electrically neutral. Why?

n-type semiconductor is formed by doping it
with pentavalent impurities. These impurities or dopant takes the atoms in the crystal and its four electrons take part in chemical bonding with four electrons of intrinsic semiconductor or pure semiconductor. Whereas the last electrons are left free. Since, as whole atom is electrically neutral, so w-type semiconductor is also neutral.