  We analyse 4.5, 8 and 24 um band Spitzer images of six gamma ray burst host
galaxies at redshifts close to 1. We constrain their star formation rates (SFR)
based on the entire available spectral energy distribution rather than the 24
um band only. Further, we estimate their stellar masses (M*) based on rest
frame K band luminosities. Our sample spans a wide range of galaxy properties:
derived SFRs range from less than 10 to a few hundred solar masses per year;
values of M* range from 10^9 to 10^10 Mo with a median of 5.6 x 10^9 Mo.
Comparing the specific star formation rate (PHI = SFR/M*) of our sample as a
function of M* to other representative types of galaxies (distant red galaxies,
Ly-alpha emitters, Lyman break galaxies, submillimeter galaxies and z ~ 2
galaxies from the Great Observatories Origins Deep Survey-North field), we find
that gamma ray burst hosts are among those with the highest PHI.
