Electrical degradation followed by breakdown was studied for thin films. A field‐assisted thermal breakdown was observed which is related to Poole‐Frenkel emission. A semiquantitative electrical degradation/breakdown model is proposed on the basis of Poole‐Frenkel emission and oxygen vacancy behavior during degradation. It is suggested that accumulation of oxygen vacancies at the cathode and acceptors at the anode forms a forward p‐n junction which increases current leading to resultant breakdown.