We present a study of the first and second switches (SWs) with nearly identical switching current I SW in Bi 2 Sr 2 Ca 0.85 Y 0.15 Cu 2 O y intrinsic Josephson junctions (IJJs). In contrast to early studies where a large difference between I 1st SW and I 2nd SW was observed, a crossover temperature T cr to the quantum phase escapes for the 2nd SW is strongly reduced (∼2.8 K) and agrees with that for the 1st SW. This confirms that the anomalous enhancement of T 2nd cr , commonly observed in the IJJs with I 1st SW < I 2nd SW , originates from the phase running state after the 1st SW. Detailed analysis of the microwave-induced escapes strongly suggests that nonlinear bifurcated phenomena possibly occurs in IJJs.Macroscopic quantum tunneling (MQT) phenomena discovered in the intrinsic Josephson junctions (IJJs) of Bi 2 Sr 2 CaCu 2 O y (Bi2212) superconductors 1) have attracted much interest for more than a decade because of the unusual properties on the MQT rate. [2][3][4][5] The most striking feature is that a crossover temperature, T cr , to the MQT state in the phase switch from the first to the second resistive branch (2nd SW) is largely enhanced compared to that from the zero voltage to the first resistive branch (1st SW) in the multi-branched current-voltage (I-V) characteristics of IJJs. 6-15) An early study 6) suggested that such an enhancement was due to the self-heating effects in the first resistive state, based on the consideration that a series array of uniform Josephson junctions should show the same value of T cr as long as the current flowing in each junction agrees with the externally-applied bias current.However, the anomalous increase of T 2nd cr was found to be independent of the device structure of IJJs with different heat-transfer environment 7) and the order of phase switches, 10) throwing doubt on the self-heating effects after the 1st SW. Detailed analyses of the switching *

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