  The $\beta$-decay properties of the neutron-deficient nuclei $^{25}$Si and
$^{26}$P have been investigated at the GANIL/LISE3 facility by means of
charged-particle and $\gamma$-ray spectroscopy. The decay schemes obtained and
the Gamow-Teller strength distributions are compared to shell-model
calculations based on the USD interaction. B(GT) values derived from the
absolute measurement of the $\beta$-decay branching ratios give rise to a
quenching factor of the Gamow-Teller strength of 0.6. A precise half-life of
43.7 (6) ms was determined for $^{26}$P, the $\beta$- (2)p decay mode of which
is described.
