We analyze Spitzer images of 30 long-duration gamma-ray burst (GRB) host galaxies. We estimate their total stellar masses (M{sub *}) based on the rest-frame K-band luminosities (L{sub K{sub r{sub e{sub s{sub t}}}) and constrain their star formation rates (SFRs; not corrected for dust extinction) based on the rest-frame UV continua. Further, we compute a mean M{sub *}/L{sub K{sub r{sub e{sub s{sub t}}} = 0.45 M{sub sun}/L{sub sun}. We find that the hosts are low M{sub *}, star-forming systems. The median M{sub *} in our sample ((M{sub *}) = 10{sup 9.7} M{sub sun}) is lower than that of 'field' galaxies (e.g., Gemini Deep Deep Survey). The range spanned by M{sub *} is 10{sup 7} M{sub sun} < M{sub *} < 10{sup 11} M{sub sun}, while the range spanned by the dust-uncorrected UV SFR is 10{sup -2} M{sub sun} yr{sup -1} < SFR < 10 M{sub sun} yr{sup -1}. There is no evidence for intrinsic evolution in the distribution of M{sub *} with redshift. We show that extinction by dust must be present in at least 25% of the GRB hosts in our sample and suggest that this is a way to reconcile our finding of a relatively lower UV-based, specific SFR ({phi} {identical_to} SFR/M{sub *}) with previous claims that GRBs have some of the highest {phi} values. We also examine the effect that the inability to resolve the star-forming regions in the hosts has on {phi}.