A study of the level structure of Si26 using in-beam γ-ray spectroscopy is presented. A full level scheme is derived incorporating all states lying below the proton threshold energy. The results are in good agreement with shell model predictions and one-to-one correspondence is found with states in the mirror nucleus Mg26. Additionally, a γ-decay branch is observed from a state at 5677.0(17) keV, which is assigned to a 1+ resonance important in the astrophysical reaction Al25(p,γ)Si26. The newly derived resonance energy, Er=159.2(35) keV, has the effect of decreasing the reaction rate at the novae ignition temperature of 0.1 GK by a factor of 2 when compared with the previous most precise measurement of this state. © 2007 The American Physical Society.