import pandas as pd
import numpy as np

d = dict( A = np.array([1,2]), B = np.array([1,2,3,4]) )
    
pd.DataFrame(dict([ (k,pd.Series(v)) for k,v in d.items() ]))

Out[7]: 
    A  B
0   1  1
1   2  2
2 NaN  3
3 NaN  4