Silveira

These cases raise a common legal question: whether, for the purpose of Social Security disability determinations, a skilled or semi-skilled work history that produced no transferable skills should be treated as equivalent to an unskilled work history. We conclude it should and reverse and remand for reconsideration.

I

Both Ernesto Silveira and Efrain Vargas challenge the Commissioner’s find *1259 ings and conclusions at the fifth step of the disability evaluation process. See Lester v. Chater, 81 F.3d 821 , 828 n. 5 (9th Cir.1996) (describing five-step sequential evaluation process); see also 20 C.F.R. §§ 404.1520 ; 416.920 (same). After a claimant has established that a severe impairment prevents the claimant from performing his or her past work, at the fifth step “the burden shifts to the [Commissioner] to show that the claimant can perform other substantial gainful work that exists in the national economy.” Swenson v. Sullivan, 876 F.2d 683, 687 (9th Cir.1989); see also Smolen v. Chater, 80 F.3d 1273, 1291 (9th Cir.1996). The Commissioner follows detailed medical-vocational guidelines in making this determination. See 20 C.F.R. pt. 404, subpt. P, app. 2; 20 C.F.R. § 416.969…