So there are a total of 12 sigma bonds and 3 pi bonds in benzene. The carbon atoms are bonded through $\mathrm{sp}^{2}-\mathrm{Sp}^{2}$ overlap while six $\mathrm{C}-\mathrm{H}$ bond is formed by $\mathrm{sp}^{2}-\mathrm{s}$ sigma bond.
Thus there is $6 \mathrm{sp}^{2}-\mathrm{s}$ sigma bond.