Compact vs semi, what cassette

Hi. Last year prior to a trip to the alps I fitted a compact chainset with an 11-28 cassette to my bike. I have now bought a semi compact for all year round riding and wanted to leave it on for the alps. Would a 11-30 on the back give me similar to the compact or would I have to go to a 32 and get a new rear mech etc to have the same ratios?

Thanks