[en] A highly enhanced regime of plasma confinement was achieved with energy confinement times up to a factor of ∼ 3 above the ITER89-P L-mode scaling for high β_p discharges with a large amount of bootstrap current up to ∼0.8 MA in JT-60U. The plasma performance in the high β enhanced confinement regime was characterized by high temperatures of T_i approx. 38 keV and T_e approx. 12 keV, a fusion neutron rate of 2.8 x 10¹⁶ n/s, a fusion product of n_i(0)τ_ET_i(0) approx. 4.4. x 10²⁰ m^-3·s·keV, Q_DD approx. 1.9 x 10^-3 and an equivalent Q_DT of ∼0.31, values that are considerably larger than those obtained in other regimes in JT-60U. The power dependence of the enhanced confinement is found to be closely coupled with the plasma current, resulting in the apparently weak dependence obtained by changing the current according to the power level. Broadening of the current profile does not appear to result in confinement deterioration, but reduces the attainable εβ_p values. The termination of the enhanced confinement phase was due to β_p collapses with ballooning-like precursors occurring at a stability limit for ideal low-n kink ballooning modes substantially below the Troyon limit. (author). 15 refs, 9 figs