Intrinsic semiconductors have a dissociated population (a bunch of
holes and electrons that separate due to temperature, and can
contribute to conduction until they recombine). Because a high
population of holes and electrons would cause a very FAST
rate of recombination (faster than thermal generation occurs) , and a very low population of holes or
electrons would cause very SLOW recombination (slower than thermal
generation of pairs), it should be no surprise that
at equilibrium, the fractional population of holes $ n_p$ and electrons $n_e$,
is related by an equation
$$constant = n_p \times n_e = n_i^2$$
where the $n_i^2$ symbolizes the at-thermal-equilibrium
numbers of holes and also of electrons.
For intrinsic silicon, $$n_p = n_e = n_i$$
Doping generates a large number of (for instance) electrons, pushing $n_e$ up,
and by the equilibrium equation, forces $n_p$ down. But, conduction
of electricity depends on the SUM of the holes and electrons. If one
has undoped material conduction is
$$K \times (n_e + n_p) = K \times 2 n_i$$
but for $n_e = 100 \times n_i$ doped material, that conduction goes
up to $$ K \times (n_e + n_p) = K \times 100.01 \times n_i$$
That's the basics (but holes are less mobile than electrons and
the real conductivity is a messier formula).
All doped silicon has more charge carriers than if it were intrinsic (undoped).
The doping level is controllable over many orders of magnitude,
which allows a wide range of properties of near pure material.
Best Answer
Conductivity of intrinsic semiconductor is due to their own internal charge carriers. The bonding between between two electrons of two neighboring atoms is covalent, therefor at NTP, there is no free charge carrier for conduction. When it is heated, some covalent bonds break due to heat and thus some electron get free for conduction. As soon as one electron gets free, there is a deficiency of electrons at its preceding position which acts as a positive charge or a hole, The number of holes is equal to number of electrons. At normal temperature, only $1$ ou of $10^9$ bonds break and therefore, conductivity is very low about few milli amps.