Investigation on the DC Stark shifts of strontium autoionization states for isotope-selective resonance ionization

•We measured for the first time the DC Stark shifts of ten Rydberg levels (neff   36–39, 50–55) of 88Sr converging to the 4d2 D3/2 limit.•The polarizability α of each level was evaluated to be |α|10−30−10−28[C2m2J−1] depending on the effective principal quantum number neff.•The residual electric field in the ionization region should be of the order of 0.1 V/cm or less for trace analysis of radioisotope 90Sr using three-step resonance excitation.•For some Rydberg levels, another nearby level was also observed with the applied electric field, implying that the DC Stark shift allows observation of forbidden transitions.